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Question
Assertion (A): Gases do not liquefy above their critical temperature, even on applying high pressure.
Reason (R): Above critical temperature, the molecular speed is high and intermolecular attractions cannot hold the molecules together because they escape because of high speed.
Options
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.
Solution
Both A and R are true and R is the correct explanation of A.
Explanation:
A real gas cannot be liquefied ‘above critical ‘ temperature, whatever pressure is applied. Intermolecular force of gas molecules is low above critical temperature.
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RELATED QUESTIONS
The critical temperature for carbon dioxide and methane are 31.1 °C and –81.9 °C respectively. Which of these has stronger intermolecular forces and why?
Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases.
| Gases | \[\ce{H2}\] | \[\ce{He}\] | \[\ce{O2}\] | \[\ce{N2}\] |
| Critical temperature in Kelvin | 33.2 | 5.3 | 154.3 | 126 |
From the above data what would be the order of liquefaction of these gases? Start writing the order from the gas liquefying first
Two different gases ‘A’ and ‘B’ are filled in separate containers of equal capacity under the same conditions of temperature and pressure. On increasing the pressure slightly the gas ‘A’ liquefies but gas B does not liquify even on applying high pressure until it is cooled. Explain this phenomenon.
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Assertion (A): At critical temperature liquid passes into gaseous state imperceptibly and continuously.
Reason (R): The density of liquid and gaseous phase is equal to critical temperature.
Why does the boundary between liquid phase and gaseous phase disappear on heating a liquid upto critical temperature in a closed vessel? In this situation what will be the state of the substance?
A gas can be liquefied:
Given below are the critical temperatures of some of the gases:
| Gas | Critical temperature (K) |
| He | 5.2 |
| CH4 | 190 |
| CO2 | 304.2 |
| NH3 | 405.5 |
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